An East Asian rail carrier needed ULSR-PDH Ring Prorection (Unidirectional Line Self-healing Ring, Plesiochronous Digital Hierarchy) for its voice and data transmissions, so that if any one E1 connection was broken the voice and data communication system would still function. This was crucial to maintaining the integrity of safety systems on a busy rail traffic facility.
Loop AM3440A units equipped with Quad E1 cards were installed at each node on the network. Signals were duplicated at each node and are sent in two different directions across the same E1 link. Upon failure of any E1 link the AM3440s are programmed to automatically switch from the primary E1 path to the redundant E1 path. In this manner, communication between any two nodes will be restored. E1 ring protection is a port based switching function with switching time of less than 50 ms.
If a break occurs on the path between the two nodes, traffic is automatically re-routed back through the ring in the other direction (ie on the redundant path) and signal integrity is maintained.
The AM3440 not only supports E1 rings but also T1 and FOM optical rings as well. The ULSR-PDH ring was based on E1 connections but also linked up to a wider SDH network with much more capacity. The management center plugged into this large network and was able to use it to manage the smaller AM3440 ring.